Arguably the most important question in the production of iN cells – in fact, in the in vitro production of all human neurons – is reproducibility between lines. We therefore assessed this question for the Ngn2-based protocol in great detail. Comparison of the gene expression profiles between iN cells produced by forced differentiation of H1 ES cells and of two independent lines of iPS cells revealed a striking concordance in expression patterns (Figs. 3B and S3D). There was no major difference between stem cells in the expression of the genes tested. The highly similar transcriptional effects of Ngn2 indicate that forced expression of Ngn2 can override presumptive epigenetic differences between various pluripotent stem cell lines to induce differentiation of a single homogenuous population of excitatory forebrain neurons.
